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Gas sorbing materials that are both reversible and highly selective are attracting increased attention due to their use in chemical sensing and chemical storage applications. In particular, the development of vapochromic materials, which exhibit pronounced color changes upon exposure to volatile organic compounds (VOCs), is advantageous because these materials can be used as visual indicators for hazardous chemicals. Stacked square-planar d8 metal complexes prove especially effective as vapochromic sensors, because the colors of these materials are strongly dependent on metal-metal separation. Intercalation of VOCs into these materials can perturb the metal-metal interactions, causing a dramatic color change. Unfortunately, most of the known vapochromic systems lack either the tunability necessary for systematic study, or suffer from the inability to produce X-ray diffraction quality crystals before and after vapor exposure. At present, the notion that one might predict vapochromic properties of materials prior to synthesis seems a distant possibility. Nevertheless, it is reasonable to envision the identification of trends and development guidelines for preparing vapochromic materials, particularly for a specific metal-ligand system